GFP_KERNEL doubt!! <was Tasklet doubt!>

Sriram Narasimhan (nsri@tataelxsi.co.in)
Sat, 12 Apr 2003 01:52:44 +0530


Hello,

The problem of allocating more than 2.5 MB was actually more or less
related to the physical memory left in the kernel.
But I moved the task which allocated the memory from the tasklet to the
keventd and used kmalloc (GFP_KERNEL).

The first time I ran my module, it failed at the same 2.5 MB limit.
I restarted the system and tried it again, and I was able to allocate 5
MB successfully.
I restarted the system and ran "free".
The report is as follows:
total used free shared buffers cached
Mem: 62264 30624 31640 0 8072 16096
-/+ buffers/cache: 6456 55808
Swap: 192772 0 192772

Then I ran gcc and compiled my code and then for the "free" report again.
The report is as follows:
total used free shared buffers cached
Mem: 62264 45320 16944 0 9256 28384
-/+ buffers/cache: 7680 54584
Swap: 192772 0 192772

I was able to notice that the physical memory had gone down though "gcc"
had completed.
The time I ran my application, I had about 2.5M physical memory left, so
I was able to allocate 2.5M.

What is happening ? What is the buffers/cache column and is there any
way I could force the kernel to release the cached memory back to free
physical ?
Is there any way I can allocate more than what is left free from the
physical memory ?

Any pointers or suggestions would be very helpful.

Thank you.
Regards,
Sriram

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